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A study on the fundamental mechanism and the evolutionary driving forces behind aerobic fermentation in yeast.

Hagman A, Piškur J - PLoS ONE (2015)

Bottom Line: The later phenomenon is called Crabtree effect and has been described in two forms, long-term and short-term effect.We determine overflow metabolism to be the fundamental mechanism behind both long- and short-term Crabtree effect, which originated approximately 125-150 million years ago in the Saccharomyces lineage.The driving force behind the initial evolutionary steps was most likely competition with other microbes to faster consume and convert sugar into biomass, in niches that were semi-anaerobic.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Lund University, Lund, Sweden.

ABSTRACT
Baker's yeast Saccharomyces cerevisiae rapidly converts sugars to ethanol and carbon dioxide at both anaerobic and aerobic conditions. The later phenomenon is called Crabtree effect and has been described in two forms, long-term and short-term effect. We have previously studied under fully controlled aerobic conditions forty yeast species for their central carbon metabolism and the presence of long-term Crabtree effect. We have also studied ten steady-state yeast cultures, pulsed them with glucose, and followed the central carbon metabolism and the appearance of ethanol at dynamic conditions. In this paper we analyzed those wet laboratory data to elucidate possible mechanisms that determine the fate of glucose in different yeast species that cover approximately 250 million years of evolutionary history. We determine overflow metabolism to be the fundamental mechanism behind both long- and short-term Crabtree effect, which originated approximately 125-150 million years ago in the Saccharomyces lineage. The "invention" of overflow metabolism was the first step in the evolution of aerobic fermentation in yeast. It provides a general strategy to increase energy production rates, which we show is positively correlated to growth. The "invention" of overflow has also simultaneously enabled rapid glucose consumption in yeast, which is a trait that could have been selected for, to "starve" competitors in nature. We also show that glucose repression of respiration is confined mainly among S. cerevisiae and closely related species that diverged after the whole genome duplication event, less than 100 million years ago. Thus, glucose repression of respiration was apparently "invented" as a second step to further increase overflow and ethanol production, to inhibit growth of other microbes. The driving force behind the initial evolutionary steps was most likely competition with other microbes to faster consume and convert sugar into biomass, in niches that were semi-anaerobic.

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Carbon-flux balance.Glucose was the main carbon and energy source for cell proliferation in all experiments. The sugar is taken up by cells, and metabolized to form biomolecules and release energy for growth. The flow of carbon in central carbon metabolism was estimated from the average formation rates in a time interval of end products such as, biomass, CO2 from fermentation and respiration, and ethanol. These output rates should be lower than or roughly equal to the input rates of carbon into a cell, which is equivalent to the average glucose uptake rates. As expected, glucose uptake rates were high for short-term Crabtree positive yeasts, which is a necessity to maintain high carbon-flux through fermentative pathways. It is clear that fermenting yeasts possessed a high glycolytic flux and at least a basal activity of enzymes that constitute the fermentative pathway. It is also clear that K. lactis, which had a glycolytic capacity close to intermediate fermenting yeast, such as L. kluyverii, L. waltii and T. franciscae only fermented weakly, and thus appeared to have a retarded response to glucose. This can however be explained by the higher anabolic flux in K. lactis, which directs the carbon flow from fermentative pathways to biomass formation.
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pone.0116942.g004: Carbon-flux balance.Glucose was the main carbon and energy source for cell proliferation in all experiments. The sugar is taken up by cells, and metabolized to form biomolecules and release energy for growth. The flow of carbon in central carbon metabolism was estimated from the average formation rates in a time interval of end products such as, biomass, CO2 from fermentation and respiration, and ethanol. These output rates should be lower than or roughly equal to the input rates of carbon into a cell, which is equivalent to the average glucose uptake rates. As expected, glucose uptake rates were high for short-term Crabtree positive yeasts, which is a necessity to maintain high carbon-flux through fermentative pathways. It is clear that fermenting yeasts possessed a high glycolytic flux and at least a basal activity of enzymes that constitute the fermentative pathway. It is also clear that K. lactis, which had a glycolytic capacity close to intermediate fermenting yeast, such as L. kluyverii, L. waltii and T. franciscae only fermented weakly, and thus appeared to have a retarded response to glucose. This can however be explained by the higher anabolic flux in K. lactis, which directs the carbon flow from fermentative pathways to biomass formation.

Mentions: To further investigate for any differences in the regulation of energy-associated metabolism and growth in short-term Crabtree positive and Crabtree negative yeasts, we investigated the differences in carbon flux through anabolic and catabolic pathways for all yeast species. This was accomplished with a carbon flux-balance, where average rates at certain time intervals for glucose consumption were compared to the average rates of carbon dioxide production (from both respiration and fermentation), ethanol production, and biomass production (Fig. 4 and Table 2). It can be shown that the initial growth rates were highly unstable during the transition from glucose limited steady-state growth to glucose excess growth in all yeasts (see also S8 Fig.). Interestingly, our flux-balance also reveals higher glucose consumption rates as compared to biomass formation and respiration in all short-term Crabtree positive yeasts. This short-term imbalance between anabolic and catabolic pathways was not observed in any of the Crabtree negative yeasts, for any of the investigated time intervals. Thus, high glucose uptake rates (that exceeded biomass formation and respiration) lead to unbalanced carbon-flux between glycolysis and anabolic pathways, what resulted in increased flux through fermentative pathways and ethanol formation in short-term Crabtree positive yeasts.


A study on the fundamental mechanism and the evolutionary driving forces behind aerobic fermentation in yeast.

Hagman A, Piškur J - PLoS ONE (2015)

Carbon-flux balance.Glucose was the main carbon and energy source for cell proliferation in all experiments. The sugar is taken up by cells, and metabolized to form biomolecules and release energy for growth. The flow of carbon in central carbon metabolism was estimated from the average formation rates in a time interval of end products such as, biomass, CO2 from fermentation and respiration, and ethanol. These output rates should be lower than or roughly equal to the input rates of carbon into a cell, which is equivalent to the average glucose uptake rates. As expected, glucose uptake rates were high for short-term Crabtree positive yeasts, which is a necessity to maintain high carbon-flux through fermentative pathways. It is clear that fermenting yeasts possessed a high glycolytic flux and at least a basal activity of enzymes that constitute the fermentative pathway. It is also clear that K. lactis, which had a glycolytic capacity close to intermediate fermenting yeast, such as L. kluyverii, L. waltii and T. franciscae only fermented weakly, and thus appeared to have a retarded response to glucose. This can however be explained by the higher anabolic flux in K. lactis, which directs the carbon flow from fermentative pathways to biomass formation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4305316&req=5

pone.0116942.g004: Carbon-flux balance.Glucose was the main carbon and energy source for cell proliferation in all experiments. The sugar is taken up by cells, and metabolized to form biomolecules and release energy for growth. The flow of carbon in central carbon metabolism was estimated from the average formation rates in a time interval of end products such as, biomass, CO2 from fermentation and respiration, and ethanol. These output rates should be lower than or roughly equal to the input rates of carbon into a cell, which is equivalent to the average glucose uptake rates. As expected, glucose uptake rates were high for short-term Crabtree positive yeasts, which is a necessity to maintain high carbon-flux through fermentative pathways. It is clear that fermenting yeasts possessed a high glycolytic flux and at least a basal activity of enzymes that constitute the fermentative pathway. It is also clear that K. lactis, which had a glycolytic capacity close to intermediate fermenting yeast, such as L. kluyverii, L. waltii and T. franciscae only fermented weakly, and thus appeared to have a retarded response to glucose. This can however be explained by the higher anabolic flux in K. lactis, which directs the carbon flow from fermentative pathways to biomass formation.
Mentions: To further investigate for any differences in the regulation of energy-associated metabolism and growth in short-term Crabtree positive and Crabtree negative yeasts, we investigated the differences in carbon flux through anabolic and catabolic pathways for all yeast species. This was accomplished with a carbon flux-balance, where average rates at certain time intervals for glucose consumption were compared to the average rates of carbon dioxide production (from both respiration and fermentation), ethanol production, and biomass production (Fig. 4 and Table 2). It can be shown that the initial growth rates were highly unstable during the transition from glucose limited steady-state growth to glucose excess growth in all yeasts (see also S8 Fig.). Interestingly, our flux-balance also reveals higher glucose consumption rates as compared to biomass formation and respiration in all short-term Crabtree positive yeasts. This short-term imbalance between anabolic and catabolic pathways was not observed in any of the Crabtree negative yeasts, for any of the investigated time intervals. Thus, high glucose uptake rates (that exceeded biomass formation and respiration) lead to unbalanced carbon-flux between glycolysis and anabolic pathways, what resulted in increased flux through fermentative pathways and ethanol formation in short-term Crabtree positive yeasts.

Bottom Line: The later phenomenon is called Crabtree effect and has been described in two forms, long-term and short-term effect.We determine overflow metabolism to be the fundamental mechanism behind both long- and short-term Crabtree effect, which originated approximately 125-150 million years ago in the Saccharomyces lineage.The driving force behind the initial evolutionary steps was most likely competition with other microbes to faster consume and convert sugar into biomass, in niches that were semi-anaerobic.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Lund University, Lund, Sweden.

ABSTRACT
Baker's yeast Saccharomyces cerevisiae rapidly converts sugars to ethanol and carbon dioxide at both anaerobic and aerobic conditions. The later phenomenon is called Crabtree effect and has been described in two forms, long-term and short-term effect. We have previously studied under fully controlled aerobic conditions forty yeast species for their central carbon metabolism and the presence of long-term Crabtree effect. We have also studied ten steady-state yeast cultures, pulsed them with glucose, and followed the central carbon metabolism and the appearance of ethanol at dynamic conditions. In this paper we analyzed those wet laboratory data to elucidate possible mechanisms that determine the fate of glucose in different yeast species that cover approximately 250 million years of evolutionary history. We determine overflow metabolism to be the fundamental mechanism behind both long- and short-term Crabtree effect, which originated approximately 125-150 million years ago in the Saccharomyces lineage. The "invention" of overflow metabolism was the first step in the evolution of aerobic fermentation in yeast. It provides a general strategy to increase energy production rates, which we show is positively correlated to growth. The "invention" of overflow has also simultaneously enabled rapid glucose consumption in yeast, which is a trait that could have been selected for, to "starve" competitors in nature. We also show that glucose repression of respiration is confined mainly among S. cerevisiae and closely related species that diverged after the whole genome duplication event, less than 100 million years ago. Thus, glucose repression of respiration was apparently "invented" as a second step to further increase overflow and ethanol production, to inhibit growth of other microbes. The driving force behind the initial evolutionary steps was most likely competition with other microbes to faster consume and convert sugar into biomass, in niches that were semi-anaerobic.

Show MeSH
Related in: MedlinePlus